High-performance polyimide materials have been used for many years as insulating covers on electrical wiring and other aerospace applications because of their excellent electrical properties, chemical resistance, and high heat performance. In wiring applications, over time this type of polyimide insulation usually undergoes slow degradation due to polymer chain breakdown via hydrolysis initiated by the presence of water vapor. Many older military and commercial aircraft, as well as spacecraft such as the Space Shuttle, have miles of electrical wire coated with polyimide insulation. As this insulation ages, it becomes much more brittle and susceptible to damage from mechanical and electrical stresses. Past experience has shown that replacement of damaged wires is both very difficult and not cost effective when compared to repairing such wiring.
Due to the chemical inertness of polyimide wire insulation, present repair techniques involve the wrapping of the damaged wire in multiple passes with tapes of materials such as TEFLON or other plastics and tying each end of the tape wrap to secure it in place. Another method for repairing damaged wire involves simply enclosing the damaged area with a low-melt “clam-shell” shaped piece of repair polymer and “shrink-wrapping” the repair material onto the damaged area. Neither of these methods is considered hermetic or permanent in forming a close, intimate bond between the repair material and the damaged polyimide insulation; consequently the repaired wire typically needs to be replaced over time. Therefore, new and better materials for repairing wire insulation are needed.
Existing adhesives are often not as strong as desired. Some adhesives are brittle after curing, so that the adhesive bond is more likely to break than the materials that are bonded together, particularly if the materials bonded together are flexible or non-brittle. Existing adhesives also, in many cases, have poor chemical resistance or cannot withstand high temperatures.
New adhesives are needed with advantageous properties such as high bonding strength, flexibility, chemical resistance, or heat stability. New methods of bonding materials are also needed.